In order to ensure that magnetic tape cassettes having highly delicate magnetic tapes will be protected in storage, special containers of various types have been provided, which contain receptacles, which are arranged one behind the other and into which the cassettes can slidably be inserted. No. EP-A1-0 162 999 corresponding to U.S. Pat. No. 4,627,535 discloses a container in which each receptacle is defined by a pair of mutually opposite tracks. To permit the cassettes to be taken more conveniently from said receptacles, said tracks of each pair define a throat and stops so that the cassettes can be tilted in said receptacles and the cassettes which have been inserted into the receptacles can be handled like blocks of a block file and can be consecutively tilted for inspection. As a result, a desired cassette can easily be found and can conveniently be taken without damage. But the receptacles of that known container are designed to accommodate unpackaged cassettes and cannot be used to accommodate cassettes contained in a unit package. Some manufacturers of magnetic tape cassettes which are mainly intended for a storage of data recommend that the delicate recording media should be protected in that each cassette is left in the plastic box or in the simpler slide-in carton box in which the cassette is delivered until the cassette is inserted into the apparatus in which it is operated for recording or playback. For this reason the cassettes stored in suitable containers should also be kept in the plastic boxes or slide-in carton boxes. For that purpose, special containers are required, which are designed in adaptation to the dimensions of the unit package to be stored so that the manufacture of such containers is more expensive, storage containers of numerous different sizes must be offered for sale and must be kept in storage by the user and the magnetic tape librarian requires a plurality of different types of containers for the storage of unpackaged and packaged magnetic tape cassettes.